UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

IN 

AGRICULTURAL    SCIENCES 

Vol.  3,  No.  2,  pp.  25-36,  plates  9-11  September  29,  1917 


OPTIMUM  MOISTURE  CONDITIONS  FOR  YOUNG 
LEMON  TREES  ON  A  LOAM  SOIL 


BY 

L.  W.  FOWLEE  and  C.  B.  LIPMAN 


Among  the  numerous  problems  emanating  from  the  use  of  irriga- 
tion water  on  land  is  the  important  one  of  maintaining  as  nearly  as 
possible  an  optimum  moisture  content  in  the  soil.  While  much 
research  work  has  been  done  in  an  attempt  to  determine  what  consti- 
tutes such  an  optimum  moisture  content,  it  seems  that  our  knowledge 
is  still  too  indefinite  for  accurate  application  to  specific  cases.  For 
that  reason  it  has  appeared  to  the  junior  author  that  some  specific 
information  should  be  gathered  concerning  the  moisture  needs  of  soils 
which  are  used  for  growing  crops  under  field  conditions  and  also  the 
variations  in  such  moisture  needs  occurring  through  changes  in  soil 
type  and  changes  in  the  kind  of  crop  grown.  Obviously  the  task  just 
mentioned  is  too  great  to  be  disposed  of  quickly,  and  in  one  series 
of  experiments,  and  it  has,  therefore,  seemed  wise  to  start  the  work 
with  one  crop  and  one  soil  type  first.  Owing  to  the  fact  that  the 
Limoneira  Company  of  Santa  Paula,  California,  expressed  its  willing- 
ness to  co-operate  in  such  an  experiment  and  to  give  to  it  the  time 
and  attention  of  the  senior  author  as  well  as  the  necessary  equipment, 
the  experiment  was  started  with  young  lemon  trees  on  a  loam  soil, 
characteristic  of  much  of  the  large  ranch  in  the  possession  of  the 
company.  It  was  further  hoped  that  the  results  obtained  from  the 
experiment,  along  with  contemporaneous  results  of  careful  moisture 
determinations  at  short  intervals  in  the  lemon  orchards,  would  give  a 
basis  for  planning  a  scientific  system  of  irrigation  in  the  orchards  in 
question.  A  plan  for  the  specific  experiment,  and  one  for  the  field 
work  were  arranged  by  the  junior  author  and  they  were  executed 
under  the  direction  of  the  senior  author.      The  detailed  results  of  the 


26  University  of  California  Publications  in  Agricultural  Sciences       [Vol.3 

field  work  cannot  be  given  in  this  paper  but  will  need  discussion 
separately  elsewhere  at  some  future  time.  The  experiment  proper, 
however,  has  now  been  in  operation  for  more  than  two  years  and  the 
results  obtained  have  been  so  interesting  as  to  more  than  justify  their 
presentation  and  discussion  here. 

Plan  of  the  Experiment 
It  was  decided  to  grow  the  young  lemon  trees  in  galvanized  iron 
cylinders,  24  inches  in  depth  and  15  inches  in  diameter.  The  cylin- 
ders were  painted  with  a  heavy  coating  of  asphalt.  The  soil  used  in 
them  is  a  loam  having  the  following  mechanical  analysis  (Bureau  of 
Soils  method),  which  was  furnished  us  through  the  courtesy  of 
Professor  C.  F.  Shaw: 

First  foot  Second  foot  Third  foot 

Fine  gravel  1.45  1.14  1.71 

Coarse  sand  3.24  3.13  4.27 

Medium  sand  3.32  3.25  4.13 

Fine  sand 12.77  12.33  12.58 

Very   fine   sand 42.99  44.93  43.22 

Silt   18.74  19.31  16.61 

Clay    17.49  15.91  17.48 

On  the  basis  of  this  mechanical  analysis  the  Bureau  of  Soils  would 
classify  the  soil  as  a  fine  sandy  loam,  but  owing  to  its  relatively  high 
clay  and  silt  content  it  should,  in  the  junior  author's  opinion,  be 
classified  as  a  light  clay  loam,  but  certainly  as  no  less  than  a  loam. 
Mr.  Chas.  A.  Jensen  of  the  Bureau  of  Plant  Industry,  United  States 
Department  of  Agriculture,  was  good  enough  to  furnish  the  ' '  moisture 
equivalents"  and  "wilting  coefficients"  of  the  first  three  feet  in  depth 
of  the  soil  used,  as  it  occurs  under  field  conditions.  Mr.  Jensen's 
determinations  follow : 

Wilting  per  cent  Moisture  equivalent 

First  foot  9.3  17.0 

Second  foot  8.7  15.9 

Third  foot 8.1  14.0 

The  soil  used  in  the  cylinders  was  obtained  from  a  lemon  orchard 
now  twenty-three  years  of  age  in  which  the  trees  have  always  shown 
good  vigor  and  high  productivity.  The  soil  from  the  first  and  second 
feet  in  depth  was  thoroughly  mixed  in  preparation  for  use  in  the 
cylinders.     The  same  amount  of  soil  was  weighed  into  every  cylinder. 

The  variety  of  lemons  selected  for  the  test  was  the  Lisbon.  The 
trees  were  one  vear  old  and  as  nearly  uniform  as  could  be  obtained. 


1917]       Fowler-Lipman :  Optimum  Moisture  Conditions  for  Lemon  Trees 


27 


Before  planting,  the  roots  of  the  trees  were  entirely  freed  from  soil 
and  the  tops  were  pruned  to  a  whip.  The  planting  was  done  on  March 
17,  1915,  after  which  the  cylinders  were  placed  in  a  row  (see  plate 
9)  in  a  trench  24  inches  deep,  in  order  to  prevent  the  undue  heating 
of  the  soil  from  the  exposure  of  the  cylinders  to  the  direct  sun.  From 
the  time  of  planting  until  June  1,  1915,  a  soil  moisture  content  of  20 
per  cent  based  on  the  dry  weight  of  the  soil  was  maintained  in  all 
the  cylinders  in  order  to  give  all  the  trees  the  same  start.  At  the 
last  date  mentioned  the  growth  of  all  the  trees  was  sufficiently  good 
and  uniform  enough  to  allow  of  the  arrangement  for  the  variation 
in  moisture  content  in  the  different  cylinders.  In  order  to  allow  for 
individual  variations  among  the  trees,  every  moisture  content  was 
employed  on  triplicate  trees  and  the  moisture  percentages  tested  were 
as  follows : 

10  per  cent  based  on  the  water-free  soil. 

io      It  it  it  it 

-lAti  i  i  it  t  I 

i  a     1 1         it  it         it 

1Q       II  t  i  it  11 

20  "  ' '  "  ' ' 
22    ' '       { t         1 1       ii 

■  >  i     tt       1 1         tt       tt 

26  "  "  "  " 
28  "  "  "  " 
30    "       "         "       " 


The  cylinders  are  weighed  three  times  per  week  and  the  losses  of 
moisture  due  to  evaporation  are  replaced  by  additions  of  the  necessary 
amounts  of  the  ordinary  irrigation  water  employed  on  the  ranch. 
The  weighing  is  done  on  steelyards  and  a  derrick  is  available  for 
raising  and  lowering  the  cylinders  as  desired.  The  water  is  added  in 
a  depression  in  the  surface  soil  corresponding  in  nature  to  an  irri- 
gation furrow  and  is  applied  by  means  of  a  very  small  stream  flowing 
from  a  hole  in  a  can  used  for  the  purpose.  This  method  is  employed 
to  obviate  puddling.  During  rainy  weather  the  cylinders  kept  at  less 
than  20  per  cent  moisture  are  protected  by  canvas  roofs.  Between 
irrigations  the  surface  of  the  soil  in  all  the  cylinders  is  kept  cultivated. 


Results  of  the  Experiment 
Seventeen  months  after  the  experiment  was  started  or  when  the 
trees  were  two  years  and  five  months  old,  measurements  were  made 
and  a  diagram  showing  their  relative  heights  at  the  time  is  given  in 


28  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  3 

figure  1.  While,  however,  the  measurements  show  clearly  enough  the 
effects  of  the  different  soil  moisture  percentages  on  the  growth  of 
the  young  lemon  trees,  they  do  not  really  tell  the  whole  story,  since 
the  general  vigor  and  abundance  of  foliage  are  naturally  as  much  and 
perhaps  more  affected  than  the  height  by  the  moisture  conditions  in 
the  soil.  For  that  reason  photographs  taken  at  about  the  time  the 
measurements  were  made  are  submitted  herewith  to  show  the  actual 
condition  of  the  trees. 

By  whatever  criterion  the  results  are  gauged,  it  is  at  once  clear 
that  the  effects  of  the  soil  moisture  content  on  the  development  of 
the  young  lemon  trees  are  most  striking.  For  the  soil  and  plant  in 
question,  20  per  cent  of  moisture  based  on  the  dry  weight  of  the  soil 
seems  to  be  optimum  in  so  far  as  the  total  growth  and  the  height  of 


Fig.  1.  Showing  the  relative  heights  of  lemon  trees  grown  with  different 
quantities  of  moisture.  Trees  29  months  old;  in  experiment  17  months.  The 
relative  heights  are  shown  on  the  ordinates  and  the  percentages  of  moisture  under 
which  they  were  produced  are  given  in  the  abscissae.  The  broken  line  shows  the 
height  of  all  the  trees  at  the  beginning  of  the  experiment. 

the  trees  are  concerned.  A  fact  which  is  not  brought  out  by  either 
the  measurements  or  the  photographs  is  that  the  general  tone  and 
color  of  the  trees  growing  in  the  20  per  cent  cylinders  is  somewhat 
inferior  to  that  of  the  trees  growing  in  the  16  per  cent  and  18  per  cent 
cylinders.  The  optimum  moisture  content  of  the  loam  studied  for 
young  Lisbon  lemons  seems  to  be  therefore  between  18  and  20  per 
cent,  if  we  may  judge  from  the  experiment  described  and  from  the 
time  given  it.  The  trees  at  or  near  the  optimum  moisture  content 
doubled  in  height  and  general  size  during  the  period  mentioned,  while 
the  trees  at  10  per  cent  or  at  30  per  cent  moisture  contents  have 
scarcely  gained  more  than  half  of  their  original  height  in  the  period 
named. 

Other  important  points  deserve  mention  in  connection  with  the 
results  obtained.      It  appears  from  the  data  given  that  the  range  of 


1917]      Fowler-Lipman:  Optimum  Moisture  Conditions  for  Lemon  Trees 


29 


soil  moisture  percentages  within  which  the  young  Lishon  trees  will 
grow  satisfactorily  in  the  soil  studied  is,  relatively  speaking,  a  wide 
one,  since  for  practical  purposes  there  is  probably  little  difference 
between  the  growth  obtained  at  moisture  percentages  varying  from 
16  to  22,  both  inclusive.  This  is  a  fortunate  circumstance  from  the 
point  of  view  of  orchard  practice  since  it  allows  of  considerable  leeway 
in  the  control  of  irrigation  operations.  It  does  not  follow,  however, 
that  as  regards  fruit  production  the  same  wide  range  of  moisture  per- 
centages in  the  soil  would  be  similarly  effective  as  in  the  case  of 
general  vegetative  growth.  On  either  side  of  the  range  of  moisture 
percentages  just  discussed,  there  can  be  no  question  that  conditions 
are  far  from  proper  for  good  tree  growth.  This  is  especially  true, 
however,  for  moisture  percentages  in  excess  of  22  per  cent,  at  which 
the  light-colored  foliage  and  general  lack  of  vigor,  increasing  with 
increase  of  moisture,  accompany  the  slow  growth.  In  the  case  of  the 
cylinders  receiving  less  than  16  per  cent  of  moisture  while  the  growth 
is  also  slow  owing  to  lack  of  moisture,  the  leaves  and  branches  appear 
to  be  normal  in  color  and  the  trees  appear  to  be  suffering  less  from 
untoward  conditions.  It  seems  to  be  very  clear  at  this  stage  of  the 
experiment,  therefore,  that,  in  practice,  there  is  very  much  more 
danger  to  young  lemon  trees  from  too  much  than  from  too  little 
moisture  in  the  soil.  The  harmful  effects  of  the  former  seem  to  be 
always  more  sharply  denned  and  more  intense ;  small  additions  of 
water  beyond  the  optimum  produce  large  and  sudden  changes,  whereas 
small  decreases  of  moisture  below  the  optimum  show  their  effects  only 
gradually  with  the  continued  reduction  in  the  moisture  percentage. 

About  six  months  have  passed  since  the  measurements  and  photo- 
graphs discussed  above  were  obtained.  The  effects  of  the  different 
moisture  percentages  continue  to  stand  out  as  clearly  or  more  so  than 
ever  before,  indicating  the  probability  that  they  may  continue  so  for 
a  long  period  of  years.  It  should  be  mentioned  here  that  small  but 
uniform  applications  of  sulphate  of  ammonia  have  been  made  to  all 
the  cylinders  during  the  past  year  to  maintain  a  more  nearly  normal 
growth  than  is  possible  without  additional  nitrogen  in  such  a  limited 
volume  of  soil  as  that  at  the  disposal  of  the  trees  in  the  cylinders. 

In  the  soil  under  study  in  this  experiment  it  was  found  that  the 
theoretical  wilting  point  was  very  close  to,  if  not  identical  with,  the 
actual  wilting  point,  as  both  the  field  moisture  determinations  and  the 
10  per  cent  moisture  cylinders  have  on  very  dry  days  attested.  It 
will   be   observed,   moreover,   that   the   moisture   equivalent   and   the 


30  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  3 

optimum  moisture  percentage  in  the  same  soil  are  not  far  apart. 
While  the  height  of  the  trees  is  greatest  at  moisture  percentages  in 
excess  of  that  of  the  moisture  equivalent,  the  most  vigorous  appearance 
of  the  trees  is  obtained  with  percentages  of  soil  moisture  very  close 
to  the  moisture  equivalent.  As  above  stated,  it  is  not  possible  now 
to  discuss  the  detailed  results  of  the  moisture  determinations  in  the 
orchard,  but  in  general  it  was  true  that  the  soil  moisture  percentages 
rarely  fell  to  the  wilting  point  in  the  orchard  soil  and  very  infre- 
quently rose  to  the  optimum  under  the  system  of  irrigation  practiced. 
In  the  orchard  under  consideration,  therefore,  a  lack  rather  than  an 
oversupply  (a  common  condition  elsewhere  in  California)  of  water 
seems  to  be  the  rule. 


1917]       Fowler— Lipman:  Optimum  Moisture  Conditions  for  Lemon  Trees  31 


Summary 
In  attempting  to  determine  the  optimum  moisture  content  of  a 
rather  heavy  loam  soil  for  young  Lisbon  lemon  trees  grown  in  cylin- 
ders, at  the  Limoneira  Ranch,  Santa  Paula,  California,  the  following 
information  was  obtained  in  the  course  of  the  first  two  years  of  the 
experiment : 

1.  A  moisture  percentage  of  20  per  cent  based  on  the  dry  weight 
of  the  soil  has  produced  the  tallest  trees. 

2.  Trees  grown  with  16  and  18  per  cent  of  moisture,  while  not  as 
tall  as  those  grown  with  20  per  cent  of  soil  moisture,  show  better  color 
and  more  vigor.      The  differences  are  not  very  marked,  however. 

3.  The  foregoing  facts  seem  to  show  that  the  range  of  optimum 
or  nearly  optimum  moisture  percentages  for  the  soil  and  plant  in 
question  is  a  relatively  wide  one. 

4.  Much  more  visible  damage  results  to  the  young  lemon  trees  from 
moisture  percentages  in  excess  of  the  optimum  than  from  those  below 
the  optimum. 

5.  Every  successive  increment  of  moisture  beyond  the  optimum 
is  accompanied  by  a  sharp  depression  in  growth,  color,  and  general 
vigor  of  the  trees. 

6.  Every  successive  decrement  of  moisture  from  the  optimum 
shows  only  a  relatively  slight  depression  in  growth. 

7.  The  theoretical  wilting  point  and  the  moisture  equivalent  for 
the  soil  studied  are  in  close  accord  respectively  with  the  actual  wilting 
point  as  determined  in  the  soil  of  the  orchard  and  the  optimum  moist- 
ure content  as  determined  in  the  experiment  discussed  above. 

The  authors  wish  to  acknowledge  their  sincerest  sense  of  obligation 
to  Messrs.  C.  C.  Teague  and  J.  D.  Culberson  of  the  Limoneira  Com- 
pany, who  have  so  kindly  cooperated  with  them  in  the  experiment 
above  described  and  who  have  at  all  times  been  willing  to  place  at 
their  disposal  all  possible  facilities  for  the  prosecution  of  the  work. 


PLATE  9 

Fig.  1.  Showing  arrangement  of  cylinder  experiment  to  study  water  needs 
of  young  lemon  trees. 

Fig.  2.  From  right  to  left,  cylinders  1,  2,  and  3  maintained  at  10  per  cent 
of  soil  moisture;  cylinders  4,  5,  and  6  maintained  at  12  per  cent  of  soil  moisture. 


[32] 


UNIV. 


CALIF.    PUBL.    AGR.    SCI.,    VOL.    3 


[FOWLER-LIPMANI    PLATE    9 


(?'■- 


:-.#-"-- 


Fig.  1 


Fiar. 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://archive.org/details/optimummoisturec32fowl 


PLATE  10 
Fig.  1.     From  right  to  left,  cylinders  1,  2,  and  3  maintained  at  14  per  cent 
of  soil  moisture,   and   cylinders  4,   5,   and   6   maintained   at   16   per   cent   of   soil 
moisture. 

Fig.  2.  From  right  to  left  again,  cylinders  1,  2,  and  3  maintained  at  18  per 
cent  of  soil  moisture,  and  cylinders  4,  5,  and  6  maintained  at  20  per  cent  of  soil 
moisture.     Part  of  cylinder  7  showing  22  per  cent  of  soil  moisture. 


[34] 


UNIV.    CALIF.    PUBL.    AGR.    SCI.,    VOL.    3 


'FOWLER-LIPMAN  |    PLATE    10 


*m 


Fig.  1 


MRU 


£&*W.  «&$&¥&■     ■** 


*3iSSfc 


Fig. 


PLATE  11 

Fig.  1.  From  right  to  left,  cylinders  1  and  2  maintained  at  22  per  cent  of 
soil  moisture,  cylinders  3,  4,  and  5  at  24  per  cent  of  soil  moisture,  cylinders  6  and 
7  at  26  per  cent  of  soil  moisture. 

Fig.  2.  From  right  to  left,  cylinder  1  at  26  per  cent  of  soil  moisture,  cylinders 
2,  3,  and  4  at  28  per  cent  of  soil  moisture,  cylinders  5,  6,  and  7  at  30  per  cent  of 
soil  moisture. 


[36] 


UNIV.    CAL 


F.    PUBL.    AGB.    SCI.,    VOL.    3  [  FOWLER-LI  PM  AN  |    PLATE    11 


3 


Fig.  1 


Fig. 


